Apparatus for flashing fluorescent lamps



APPARATUS FOR FLASHING FLUURESCENT LAMPS Delmar D. Kershaw, HighlandHeights, Ollio, assigner to General Electric Company, a corporation ofNew York Application March 26, 1956, Serial No. 573,79@

14 Claims. (Cl. 315-98) My invention relates to apparatus forV flashingfluorescent lamps repetitively between on and ofi conditions or betweentwo stable conditions of different luminous intensity such as may beused, for example, in flashing sign applications.

Apparatus for flashing fluorescent lamps has not in the past found widecommercial application principally because of problems of life andreliability. When operated with conventional ballasts and flashers, thesevere duty placed upon the fluorescent lamps by such frequent startingand stopping with the consequent frequent ionization and partial ortotaldeionization of the gas within the lamps causes the lamps quickly toburn out. In addition, starting has not always been instantaneous sothat the flashing cycle has not been reliable.

Accordingly, a general object of the invention is to provide apparatusfor flashingfiuorescent lamps having improved life and reliability.

Another object of the invention is to provide apparatus for flashingfluorescent lamps in which the energy shock to the components, andparticularly to the lamps, during the flashing periods is reduced,thereby to improve the life and reliability of these components.

A further object is to provide a high-reactance transformer suitable foruse in apparatus for flashing hotcathode fluorescent lamps.

In general, in accord with my invention, a high-reactance transformer orballast and a flasher switch are arranged for connection between analternating-current source and a fluorescent lamp of the hot-cathodetype to ignite and control the current to the lamp. Heating windings onthe transformer are constructed for continuously heating the cathodes tostatic temperatures (without lamp discharge) considerably above thenormal or rated static temperatures when the lamp is used for generallighting applications. I have discovered that this elevation in thestatic temperature of the cathodes results in an improvement in the lifeof the lamp as well as greater reliability in starting when the lamp isrepetitively flashed. It will be appreciated that if the cathodes of thelamp were operated at this elevatedstatic temperature in applicationswhere the lamp was lighted continuously, or

for long periods of time, the lamps would prematurely burn out. Y y

In accord with a further feature of the invention, an impedance elementis preferably connected in parallel with the flasher switch for passingat least asmall current to the lamp during open periods of theA switch.Since lamp current is not completelyextinguished every few seconds, thegas around the cathodes or filaments of the lamps does not becomecompletely deionized andV restarting is facilitated and not such asevere shock to the lamp. In addition, since the flasher switch doesAnot interrupt full current, the duty on the switch as well as thetendency to Y arc across its contacts is substantially reduced therebyprolonging the life of the switch.

Vl'he novel featuresbelieved characteristic of ther in*` Patented Oct.28, 1958 ICC vention are set forth in the appended claims. The inventionitself, however, together with further objects and advantages thereofwill be easily understood by referring to the following descriptiontaken in connection with the accompaniing drawing in which the solefigure is va circuit diagram of apparatus embodying one form of theinvention.

Referring to the drawing, there is shown a high-reactance inductivedevice in the form of a ballast transformer 10 connected in circuit witha repeating or flasher switch 11 to receive power through inputterminals 12 and to control the current to a fluorescent lamp 13. The

term asher switch is used herein to connote any switch whichrepetitively and cyclically opens and closes a pair of contacts to makeand break the circuit with opened and closed flashing periods of lessthan one minute duration. Ballast transformer 10 has a primary winding14 and a secondary winding 15 arranged on discrete portions of a centralelongated leg 16 of its magnetic core. These windings are surrounded byyoke-core portions 17 having inwardly directed sections 18 betweenwindings 14 and 15 extending into close proximity with the central coreleg 16 to form magnetic-flux-shunting paths therewith and thereby toprovide the desired highinductive reactance for ballasting the lamp.VFluorescent lamp 13 is of the hot-cathode type as shown, havingthermionic filamentary activated electrodes for cathodes Ztl, 21 atopposite ends adapted to be continuously energized by heating windings22 and 23 arranged on the' primary winding section of transformer 10.Lamp 13 is mounted in close proximity with thegrounded'electricconducting plate or strip member 24 to facilitatestarting. Primary winding 14 is connected across input terminals 12through a disconnecting-type socket 25 for one end of lamp 13. Removal'of lamp 13 from socket 25 functions to disconnect lead 26 from filamentlead 27 thereby to interrupt power to primary winding 14.

Flasher switch 11 is shown as a 'thermally flexing bimetal switch butmay be of anyconventional type such as those employing a motor rotatinga cam which opens and closes the switch contacts every few seconds.Flasher switch 11 is connected in series circuit with lamp `13 tocontrol the current supplied thereto. Preferably, switch 11 isconnected, as shown, between the high-voltage end of primary winding 14and the low-voltage end of secondary winding 15. In this way, lamp 13 isconnected to be energized by an autotransformer circuit includingprimary winding 14, flasher switchll and secondary winding 15 connectedin series.

In the ballast, a small capacitor 29 is connected between the heatingwindings 22 and 23 and a resistance 28 is connected from one winding tothe ballast case and thence to ground in order to suppress generation ofhighfrequency radiations.

In accord with one aspect of the invention, an impedance element 30 ispreferably connected in parallelcircuit relation with, for example, bybeing directly connected across the terminals of, flasher switch 11.Impedance element 30 is preferably a resistor, as shown, but mayalternatively be a capacitor or inductor.A

In accord with the invention heating windings 22 and 23 of transformerlil are constructed to applyvoltageV across the heating filaments of thecathodes 20, 21 of the lamps considerably higher than the conventionalcontinuously applied voltage thereby to increasethe current through thewindings .sufficiently to elevate the static temperature of the cathodesconsiderably above their normal or Vrated static temperatures. TheVphrase static temperature of the cathodef isused hereinto mconnote thetemperature at the hottest point of the cathode when the cathode iscontinuously heatedA by exf c. n I.. r

ternally applied voltage in the absence of a lamp discharge. The phraserated static temperature of the cathode is used herein to connote thetemperature at the hottest point of the cathode in .the absence of lampdischarge when the cathodes are continuously heated by appliedrvoltageequal Vto the rated voltage as stated or recommended by the lampmanufacturer for use in normal lighting lapplications where the lamp maybe lighted for widely varying or prolonged periods of time.

More specifically, one type of Widely used hot-'cathode lamp known asthe rapid start lamp is adapted for continuous heating by a steady-statecathode voltage rated for normal lighting applications at about 3.6volts. The cathodes of these rapid-start lamps achieve statictemperatures of about 650-degrees centigrade under such rated voltagesand without lamp discharge at which ternperatures the lamp usually burnsout in about 24 hours when flashed. In accord with my invention, l havefound lthat by increasing the number of turns on the heating windings22, 23 of transformer 10 from the ncrmal 30 turns to about 35 turns toapply a cathode voltage of about 4.6 volts, instead of the usual 3.6volts, the static temperatures of the cathodes are increased to aboutS60-degrees centigrade and fluorescent lamp life and reliability areappreciably increased when these lamps are flashed lby suitable flashingapparatus,'such as shown in Figure l. lTests show that the number ofinstantaneous starts before burn `out in lamps operating with suchhigher static-cathode temperatures is several hundred times the numberof instantaneous starts before burn out in lamps operating under normalor rated static-cathode temperatures. The range of appreciableimprovement is where the cathodes achieve static temperatures from80G-degrees centigrade to 930-degrees centigrade which, in rapid startfluorescent lamps, corresponds to an applied voltage range from 4 to5.25 volts.

The reason for this phenomenal improvement is believed to be a reductionin the intensity of ion bombardment of the cathode during starting dueto the increased cathode temperature and the consequent decrease in thepotential difference, commonly called cathode fall between the cathodeand the plasma of the lamp.

In the operation of the circuit of Figure l, the voltage across theautotransformer-connected windings 14 and with switch 11 closed issufficient to ignite fluorescent lamp 13. Once lamp 13 fires, the highreactance of the secondary winding portion of transformer 10 providesthe necessary ballasting action compensating for the negative-resistancecharacteristic of the lamp. When the contacts of flasher switch 11 opendue to the flexure of the thermally-sensitive element therein, thecurrent through the secondary-winding portion of the autotransformer andconsequently through lamp 13 is limited by the magnitude of theimpedance element 30. Impedance element 30 is particularly valuable inimproving the reliability and life where the starting voltage from thetransformer is only slightly greater than the rated ignition voltage ofthe lamp involved. The ohmic value of the impedance element 30 isselected to give the desired reduction in lamp brightness withoutextinguishing the current flowing through the lamp 13. By properselection of the impedance element 30 it has been found possiblesubstantially to completely extinguish the light emitted from lamp 13without extinguishing the current flowing therethrough. In order toobtain the benefits of more reliable starting, however, the impedance ofelement 30 should not be so large as to limit the lamp current to lessthan one half of one percent of the operating lamp current when the lampis at normal brilliance. Typical values of impedance element 30 forcontrolling a 40-watt hot-cathode fluorescent lamp are from 30,000 to50,000 ohms to give a lamp current during the off periods of switch 11of about three milliampers, corre- 4 sponding to about one percent ofrated light output of the lamp.

The life of a 40-watt rapid start lamp using the circuit described abovewith a flashing cycle of one second on and one second off has exceededl2-ml1ion flashes. With ballast circuits where a single ballasttransformer controls the current to more than one lamp connected inseries, it will be appreciated that the impedance element 30 connectedin parallel with flasher switch 11 controlling the series current tothese lamps must be proportionally smaller to provide the desiredminimum lamp current.

While I have described above a particular embodiment of the invention,many modifications may be made. It is to be understood, therefore, thatI intend, by the appended claims, to cover all such modifications asfall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. Apparatus for flashing a fluorescent lamp of the hot-cathode typefrom an alternating-current source, cornprising a high-reactancetransformer for connection between said source and said lamp to igniteand ballast said lamp, said transformer having a pair of cathodeheatingwindings constructed to supply heating current to the respective lampcathodes suflicient to elevate the static temperatures of said cathodesconsiderably above their rated static temperatures for normal lightingapplications, and a flasher switch connected in series with saidtransformer to control current to said lamp.

2. The apparatus of claim 1 including an impedance element connected inparallel circuit with said switch for passing current to said lampduring open periods of said switch.

3. Apparatus for flashing a hot-cathode fluorescent lamp from a sourceof alternating current comprising a high-reactance ballast transformerfor connection to said lamp having a primary winding for connectionacross said source, a secondary winding making autotransformerconnection with said primary winding and a pair of heating windings forconnection to the cathodes of said lamp, said heating windings beingconstructed to apply heating voltage to the lamp cathodes sullicient toraise the static temperature of said cathodes considerably above-theirrated static temperatures, and a flasher switch connected in series withsaid secondary winding for controlling current to said lamp.

4. The apparatus of claim 3 wherein said heating wind-' ings areconstructed to apply heating voltage to the lamp cathodes sufficient toraise the static temperature of lsaid cathodes to between SOO-degreesand 930-degrees centigrade.

5. The apparatus of claim 3 including an impedance element connectedacross said flasher switch for passing current to said lamp during openperiods of said switch.

6. Apparatus for flashing a hot-cathode fluorescent lamp from a sourceof alternating current comprising a ballast transformer for connectionto said lamps and having a primary winding for connection across saidsource, a -secondary winding, and heater windings for connection tothe'cathodes of said lamp, said heating windings being constructed tosupply heating current to the lamp cathodes sufficient to raise thestatic temperatures of said cathodes considerably above their ratedstatic temperatures for general lighting applications, a flasher switchmaking autotransformer connection between said primary and secondarywinding to control current to said lamp, and an impedance connectedacross said flasher switch for passing current to said lamp during openperiods of said switch.

7. Apparatus for flashing a hot-cathode fluorescent lamp from a sourceof alternating current comprising a high-reactance ballast transformerhaving a primary winding for connection across said source, a secondarywinding for connection to said lamp, Vand heating windings' forconnection to the cathodes of said lamp, a flasher switch in seriescircuit relation with said secondary winding to control current to saidlamp, and an impedance connected in parallel-circuit relation with saidasher switch for passing a small current to said lamp during openperiods of said switch.

8. The apparatus of claim 7 wherein said impedance element has animpedance suflicient to pass a current in the neighborhood of onepercent of rated-lamp current during said open period of said switch.

9. Apparatus' for ashing a uorescent lamp comprising a high-reactancedevice for connection between said source and said lamp to energize andballast said lamp, a asher switch connected in series circuit with saiddevice to control current to said lamp, and an impedance elementconnected in parallel circuit with said asher switch for passing currentto said lamp during open periods of said switch.

l0. In combination, a hot-cathode fluorescent lamp, a high-reactanceballast transformer having a primary winding for connection across asource of alternating current, a secondary winding connected to saidlamp and heating windings connected to the cathodes of said lamp andproportioned to supply current thereto to achieve a temperature in saidcathodes from 80G-degrees centigrade to 930degrees centigrade in theabsence of a discharge through said lamp, and a asher switch connectedin circuit with said secondary winding to control discharge currentthrough said lamp.

1l. The apparatus of claim l0 including an impedance element connectedin parallel with said switch for passing current to said lamp duringopen periods of said switch.

12. A high-reactance transformer for use in apparatus for ashing afluorescent lamp of the hot-cathode type comprising a magnetic corehaving a primary winding for connection to said source, a secondarywinding, and a pair of cathode-heating windings, said cathode heatingwindings being wound over the primary winding and constructed to supplyheating voltages across the respective cathodes of a lamp in the rangeof from 4 to t5.25 volts to achieve a lamp cathode static temperature inthe range of G-degrees to 930-degrees centigrade.

l3. Apparatus for flashing a uorescent lamp of the hot cathode type froman alternating current source comprising a high reactance transformerfor connection between said source and said lamp to ignite and ballastsaid lamp, said transformer having a pair of cathode heating windingsconstructed to supply heating voltage to the respective lamp cathodessucient to elevate the static temperatures of said cathodes considerablyabove their rated static temperatures for normal lighting applications,and hashing means for periodically and cyclically interrupting currentto said lamp from said transformer with hashing periods less than oneminute duration.

l4. The apparatus of claim 13 wherein said heating windings areconstructed to apply heating voltage to the lamp cathodes suicient toraise the static temperature of said cathodes to between 800 and 930centigrade.

References Cited in the file of this patent UNITED STATES PATENTS1,913,504 Nachurnsohn June 13, 1933 1,996,212 Pettet Apr. 2, 19352,422,280 Abernathy June 17, 1947 2,665,394 Arvidsson et al Ian. 5, 1954UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.,2,858,478 October 28, 1958 Delmar D. Kershaw It is hereby certified thaterror appears in thev printed specification of the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected belowo Column 2, line 29, after the numeral "23 insert aperiod; line 29, before "arranged" insert These heating windings 22 .and23 are' en; line 30, after the numeral "l0" and before the period insertm and preferably wound over thel primary winding as illustrated so .asto be closely `coupled magnetically with theA primary Winding 14 en;lcolumn 4, line' 25, after "constructed" insert im and arranged am; lineafter "supply" insert d and maintain am; line 30 before "said" insert--fla'sh line 42, after "being" inse-rt e alose'ly coupled to saidprimary Winding and being me; column 5, line 14, after "with" insert uthe output of line 19.,v after "1amp and before the comma insert m ofthe rapid start type be; column o, line 16y after constructe'd' insertwand arranged same line after "Supply" insert and maintai een Signed andsealed this 21st day of July 1959;,

(SEAL) Attest:

KARL H. A'PCLINE Attesting Officer ROBERT G.; WHISON Commissioner ofPatents

